Download of libpng 1.6.16 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. This free Mac application is a product of Greg Roelofs. Libpng for Mac lies within Design & Photo Tools, more precisely Viewers & Editors. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe.
From the developer:
This is an open source project to develop and maintain the reference library for use in applications that read, create, and manipulate PNG (Portable Network Graphics) raster image files. libpng is the official PNG reference library. It supports almost all PNG features, is extensible, and has been extensively tested for over 22 years.
You may want to check out more software for Mac, such as Cuadro or Resize Now, which might be related to libpng.